Network Working Group M. Douglass
Internet-Draft RPI
Intended status: Standards Track C. Daboo
Expires: June 13, 2015 Apple
December 10, 2014
Time Zone Data Distribution Service
draft-ietf-tzdist-service-04
Abstract
This document defines a time zone data distribution service that
allows reliable, secure and fast delivery of time zone data to client
systems such as calendaring and scheduling applications or operating
systems.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on June 13, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions . . . . . . . . . . . . . . . . . . . . . . . 4
2. Architectural Overview . . . . . . . . . . . . . . . . . . . 4
3. General Considerations . . . . . . . . . . . . . . . . . . . 6
3.1. Time Zone . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Time Zone Data . . . . . . . . . . . . . . . . . . . . . 6
3.3. Time Zone Data Server . . . . . . . . . . . . . . . . . . 7
3.4. Observance . . . . . . . . . . . . . . . . . . . . . . . 7
3.5. Time Zone Identifiers . . . . . . . . . . . . . . . . . . 7
3.6. Time Zone Aliases . . . . . . . . . . . . . . . . . . . . 7
3.7. Time Zone Localized Names . . . . . . . . . . . . . . . . 8
3.8. Truncating Time Zones . . . . . . . . . . . . . . . . . . 8
4. Time Zone Data Distribution Service Protocol . . . . . . . . 9
4.1. Server Protocol . . . . . . . . . . . . . . . . . . . . . 9
4.1.1. Time Zone Queries . . . . . . . . . . . . . . . . . . 10
4.1.2. Time Zone Formats . . . . . . . . . . . . . . . . . . 10
4.1.3. Time Zone Localization . . . . . . . . . . . . . . . 10
4.1.4. Conditional Time Zone Requests . . . . . . . . . . . 10
4.1.5. Expanded Time Zone Data . . . . . . . . . . . . . . . 12
4.1.6. Server Requirements . . . . . . . . . . . . . . . . . 12
4.1.7. Error Responses . . . . . . . . . . . . . . . . . . . 12
4.1.8. Extensions . . . . . . . . . . . . . . . . . . . . . 12
4.2. Client Guidelines . . . . . . . . . . . . . . . . . . . . 13
4.2.1. Discovery . . . . . . . . . . . . . . . . . . . . . . 13
4.2.1.1. Time Zone Data Distribution Service SRV Service
Labels . . . . . . . . . . . . . . . . . . . . . 13
4.2.1.2. Time Zone Data Distribution Service TXT records . 14
4.2.1.3. Time Zone Data Distribution Service Well-Known
URI . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.1.3.1. Example: well-known URI redirects to actual
context path . . . . . . . . . . . . . . . . 15
4.2.2. Initial Synchronization of All Time Zones . . . . . . 15
4.2.3. Subsequent Synchronization of All Time Zones . . . . 15
5. Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1. "capabilities" Action . . . . . . . . . . . . . . . . . . 16
5.1.1. Example: Get Capabilities . . . . . . . . . . . . . . 16
5.2. "list" Action . . . . . . . . . . . . . . . . . . . . . . 18
5.2.1. Example: List time zone identifiers . . . . . . . . . 19
5.3. "get" Action . . . . . . . . . . . . . . . . . . . . . . 20
5.3.1. Example: Get time zone data . . . . . . . . . . . . . 22
5.3.2. Example: Conditional Get time zone data . . . . . . . 22
5.3.3. Example: Get time zone data using a time zone alias . 23
5.3.4. Example: Get truncated time zone data . . . . . . . . 23
5.3.5. Example: Get a non-existent time zone data . . . . . 24
5.4. "expand" Action . . . . . . . . . . . . . . . . . . . . . 25
5.4.1. Example: Expanded JSON Data Format . . . . . . . . . 26
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5.5. "find" Action . . . . . . . . . . . . . . . . . . . . . . 27
5.5.1. Example: Find action . . . . . . . . . . . . . . . . 28
6. JSON Definitions . . . . . . . . . . . . . . . . . . . . . . 30
6.1. capabilities action response . . . . . . . . . . . . . . 30
6.2. list/find action response . . . . . . . . . . . . . . . . 32
6.3. expand action response . . . . . . . . . . . . . . . . . 34
7. New iCalendar Properties . . . . . . . . . . . . . . . . . . 36
7.1. Time Zone Upper Bound . . . . . . . . . . . . . . . . . . 36
7.2. Time Zone Identifier Alias Property . . . . . . . . . . . 37
8. Security Considerations . . . . . . . . . . . . . . . . . . . 37
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38
9.1. Service Actions Registration . . . . . . . . . . . . . . 38
9.1.1. Service Actions Registration Procedure . . . . . . . 38
9.1.2. Registration Template for Actions . . . . . . . . . . 39
9.2. Initial Time Zone Data Distribution Service Registry . . 39
9.2.1. Actions Registry . . . . . . . . . . . . . . . . . . 40
9.3. timezone Well-Known URI Registration . . . . . . . . . . 40
9.4. Service Name Registrations . . . . . . . . . . . . . . . 40
9.4.1. timezone Service Name Registration . . . . . . . . . 40
9.4.2. timezones Service Name Registration . . . . . . . . . 41
9.5. tzdist URN sub-namespace . . . . . . . . . . . . . . . . 41
9.6. iCalendar Property Registrations . . . . . . . . . . . . 41
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 42
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 42
11.1. Normative References . . . . . . . . . . . . . . . . . . 42
11.2. Informative References . . . . . . . . . . . . . . . . . 44
Appendix A. Change History (to be removed prior to publication
as an RFC) . . . . . . . . . . . . . . . . . . . . . 44
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47
1. Introduction
Time zone data typically combines a coordinated universal time (UTC)
offset with daylight saving time (DST) rules. Time zones are
typically tied to specific geographic and geopolitical regions.
Whilst the UTC offset for particular regions changes infrequently,
DST rules can change frequently and sometimes with very little notice
(maybe hours before a change comes into effect).
Calendaring and scheduling systems, such as those that use iCalendar
[RFC5545], as well as operating systems, critically rely on time zone
data to determine the correct local time. As such they need to be
kept up to date with changes to time zone data. To date there has
been no fast and easy way to do that. Time zone data is often
supplied in the form of a set of data files that have to be
"compiled" into a suitable database format for use by the client
application or operating system. In the case of operating systems,
often those changes only get propagated to client machines when there
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is an operating system update, which can be infrequent, resulting in
inaccurate time zone data being present for significant amounts of
time.
This specification defines a time zone data distribution service
protocol that allows for fast, reliable and accurate delivery of time
zone data to client systems. This protocol is based on HTTP
[RFC7230] using a simple JSON [RFC7159] based API.
This specification does not define the source of the time zone data.
It is assumed that a reliable and accurate source is available. One
such source is the IANA hosted time zone database [RFC6557].
Discussion of this document should take place on the tzdist working
group mailing list .
1.1. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Unless otherwise indicated, [RFC3339] UTC date-time values use a "Z"
suffix, and not fixed numeric offsets.
2. Architectural Overview
The overall process for the delivery of time zone data can be
visualized via the diagram shown below.
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==================== ====================
(a) | Contributors | | Contributors |
==================== ====================
| |
==================== ====================
(b) | Publisher A | | Publisher B |
==================== ====================
|
====================
(c) | Provider |
====================
/ | \
/ | \
==================== | ====================
(d) | Provider | | | Provider |
==================== | ====================
| | | |
| | | |
========== ========== ========== ==========
(e) | Client | | Client | | Client | | Client |
========== ========== ========== ==========
Figure 1: Time Zone Data Distribution Service Architecture
The overall service is made up of several layers:
(a) Contributors: Individuals, governments or organizations which
provide information about time zones to the publishing process.
There can be many contributors.
(b) Publishers: Publishers aggregate information from contributors,
determine the reliability of the information and, based on that,
generate time zone data. There can be many publishers, each
getting information from many different contributors. In some
cases a publisher may choose to "re-publish" data from another
publisher.
(c) Root Providers: Servers which obtain and then provide the time
zone data from publishers and make that available to other servers
or clients. There can be many root providers. Root providers can
choose to supply time zone data from one or more publishers.
(d) Secondary Providers: Servers which handle the bulk of the
requests and reduce the load on root servers. These will
typically be simple caches of the root server, located closer to
clients. For example a large Internet Service Provider (ISP) may
choose to setup their own secondary provider to allow clients
within their network to make requests of that server rather than
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making requests of servers outside their network. Secondary
servers will cache and periodically refresh data from the root
servers.
(e) Clients: Applications, operating systems etc., that make use of
time zone data and retrieve that from either root or secondary
providers.
Some of those layers may be coalesced by implementors. For example,
a vendor may choose to implement the entire service as a single
monolithic virtual server with the address embedded in distributed
systems. Others may choose to provide a service consisting of
multiple layers of providers, many secondary servers and a small
number of root servers.
This specification is concerned only with the protocol used to
exchange data between providers and from provider to client. This
specification does not define how contributors pass their information
to publishers, nor how those publishers vet that information to
obtain trustworthy data, nor the format of the data produced by the
publishers.
3. General Considerations
This section defines several terms and explains some key concepts
used in this specification.
3.1. Time Zone
A description of the past and predicted future timekeeping practices
of a collection of clocks that are intended to agree.
Note that the term "time zone" does not have the common meaning of a
region of the world at a specific UTC offset, possibly modified by
daylight saving time. For example, the "Central European Time" zone
can correspond to several time zones "Europe/Berlin", "Europe/Paris",
etc., because subregions have kept time differently in the past.
3.2. Time Zone Data
Data that defines a single time zone, including an identifier, UTC
offset values, DST rules, and other information such as time zone
abbreviations.
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3.3. Time Zone Data Server
A server implementing the Time Zone Data Distribution Service
Protocol defined by this specification.
3.4. Observance
Data that defines a portion of a time zone where the UTC offset is a
constant. A time zone with varying rules for the UTC offset will
have many adjacent observances, with the total set covering the range
of validity of the time zone data.
3.5. Time Zone Identifiers
Time zone identifiers are unique names associated with each time
zone, as defined by publishers. The iCalendar [RFC5545]
specification has a "TZID" property and parameter whose value is set
to the corresponding time zone identifier, and used to identify time
zone data and relate time zones to start and end dates in events,
etc. This specification does not define what format of time zone
identifiers should be used. It is possible that time zone
identifiers from different publishers overlap, and there might be a
need for a provider to distinguish those with some form of
"namespace" prefix identifying the publisher. However, development
of a standard (global) time zone identifier naming scheme is out of
scope for this specification.
3.6. Time Zone Aliases
Time zone aliases map a name onto a time zone identifier. For
example "US/Eastern" is usually mapped on to "America/New_York".
Time zone aliases are typically used interchangeably with time zone
identifiers when presenting information to users.
A time zone data distribution service needs to maintain time zone
alias mapping information, and expose that data to clients as well as
allow clients to query for time zone data using aliases. When
returning time zone data to a client, the server returns the data
with an identifier matching the query, but it can include one or more
additional identifiers in the data to provide a hint to the client
that alternative identifiers are available. For example, a query for
"US/Eastern" could include additional identifiers for "America/
New_York" or "America/Montreal".
The set of aliases may vary depending on whether time zone data is
truncated (see Section 3.8). For example, a client located in the US
state of Michigan may see "US/Eastern" as an alias for "America/
Detroit" whereas a client in the US state of New Jersey may see it as
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an alias for "America/New_York", and all three names may be aliases
if time zones are truncated to post-2013 data.
3.7. Time Zone Localized Names
Localized names are names for time zones which can be presented to a
user in their own language. Each time zone may have one or more
localized names associated with it. Names would typically be unique
in their own locale as they might be presented to the user in a list.
Localized names are distinct from abbreviations commonly used for UTC
offsets within a time zone. For example, the time zone "America/
New_York" may have the localized name "Nueva York" in a Spanish
locale, as distinct from the abbreviations "EST" and "EDT" which may
or may not have their own localizations.
A time zone data distribution service might need to maintain
localized name information, for one or more chosen languages, as well
as allow clients to query for time zone data using localized names.
3.8. Truncating Time Zones
Time zone data can contain information about past and future UTC
offsets that may not be relevant for a particular server's intended
clients. For example, calendaring and scheduling clients are likely
most concerned with time zone data that covers a period for one or
two years in the past on into the future, as users typically create
only new events for the present and future. Similarly, time zone
data might contain a large amount of "future" information about
transitions occurring many decades into the future. Again, clients
might be concerned only with a smaller range into the future, and
data past that point might be redundant.
To avoid having to send unnecessary data, servers can choose to
truncate time zone data to a range determined by start and end point
date and time values, and provide only offsets and rules between
those points. If such truncation is done, the server MUST include
the ranges it is using in the "capabilities" action response (see
Section 6.1), so that clients can take appropriate action if they
need time zone data for times outside of those ranges.
The truncation points at the start and end of a range are always a
UTC date-time value, with the start point being "inclusive" to the
overall range, and the end point being "exclusive" to the overall
range (i.e., the end value is just past the end of the last valid
value in the range). A server will advertise a truncation range for
the truncated data it can supply, or provide an indicator that it can
truncate at any start or end point to produce arbitrary ranges. In
addition, the server can advertise that it supplies untruncated data
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- that is data that covers the full range of times available from the
source publisher. In the absence of any indication of truncated data
available on the server, the server will supply only untruncated
data.
When truncating the start of a "VTIMEZONE" component, the server MUST
include either a "STANDARD" or "DAYLIGHT" sub-component with a
"DTSTART" property value that matches the start point of the
truncation range, and appropriate "TZOFFSETFROM" and "TZOFFSETTO"
properties to indicate the correct offset in effect right before and
after the truncation range start point. This sub-component, which is
the first observance defined by the time zone data, thus represents
the earliest valid date-time covered by the time zone data in the
truncated "VTIMEZONE" component.
When truncating the end of a "VTIMEZONE" component, the server MUST
include a "TZUNTIL" iCalendar property (Section 7.1) in the
"VTIMEZONE" component to indicate the end point of the truncation
range.
4. Time Zone Data Distribution Service Protocol
4.1. Server Protocol
The time zone data distribution service protocol uses HTTP [RFC7230]
for query and delivery of data. The interactions with the HTTP
server can be broken down into a set "actions" that define the
overall function being requested (see Section 5). Each action
targets a specific HTTP resource using the GET method, with various
request-URI parameters altering the behavior as needed.
The HTTP resources used for requests will be identified via URI
templates [RFC6570]. The overall time zone distribution service has
a "context path" request-URI defined as "{/service-prefix}". This
"root" prefix is discovered by the client as per Section 4.2.1.
Request-URIs that target time zone data directly use the prefix
"{/service-prefix,data-prefix}". The second component of the prefix
template can be used to introduce additional path segments in the
request-URI to allow for alternative ways to "partition" the time
zone data. For example, time zone data might be partitioned by
publisher release dates, or version identifiers. This specification
does not define any partitions, which is left for future extensions.
When the "data-prefix" variable is empty, the server is expected to
return the current version of time zone data it has for all
publishers it supports.
All template-URI variable values, and URI request parameters that
contain text values, MUST be encoded using the UTF-8 [RFC3629]
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character set. All responses MUST return data using the UTF-8
[RFC3629] character set. It is important to note that any "/"
characters, which are frequently found in time zone identifiers, are
percent-encoded when used in the value of a path segment expansion
variable in a URI template (as per Section 3.2.6 of [RFC6570]). Thus
the time zone identifier "America/New_York" would appear as
"America%2FNew_York" when used as the value for the "{/tzid}" URI
template variable defined later in this specification.
Most security considerations are already handled adequately by HTTP.
However, given the nature of the data being transferred and the
requirement it be correct, all interactions between client and server
SHOULD use an HTTP connection protected with TLS [RFC5246] as defined
in [RFC2818].
4.1.1. Time Zone Queries
Time zone identifiers, aliases or localized names can be used to
query for time zone data. This will be more explicitly defined below
for each action. In general however, if a "tzid" URI template
variable is used, then the value may be an identifier or an alias.
When the "pattern" URI query parameter is used it may be an
identifier, an alias or a localized name.
4.1.2. Time Zone Formats
The default media type [RFC2046] format for returning time zone data
is the iCalendar [RFC5545] data format. In addition, the iCalendar-
in-XML [RFC6321], and iCalendar-in-JSON [RFC7265] representations are
also available. Clients use the HTTP Accept header field (see
Section 5.3.2 of [RFC7231]) to indicate their preference for the
returned data format. Servers indicate the available formats that
they support via the "capabilities" action response (Section 5.1).
4.1.3. Time Zone Localization
As per Section 3.7, time zone data can support localized names.
Clients use the HTTP Accept-Language header field (see Section 5.3.5
of [RFC7231]) to indicate their preference for the language used for
localized names in the response data.
4.1.4. Conditional Time Zone Requests
When time zone data changes, it needs to be distributed in a timely
manner because changes to local time offsets might occur within a few
days of the publication of the time zone data changes. Typically,
the number of time zones that change is small, whilst the overall
number of time zones can be large. Thus, when a client is using more
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than a few time zones, it is more efficient for the client to be able
to download only those time zones that have changed.
To support conditional time zone requests, based on whether the
underlying time zone data has changed, the server supports two
options: a timestamp based synchronization mechanism, and HTTP ETag
based conditional requests (as per [RFC7232]).
For timestamp based synchronization, when a client requests a list of
all time zones, a timestamp is returned by the server, and that
serves as a synchronization "token" for later requests. Clients can
use a timestamp token in a conditional "list" action (see
Section 5.2) to limit the results to time zones which have changed
since the previous request that returned the timestamp token. A new
timestamp is then returned with the results, and that can be used in
a subsequent request. This allows clients to periodically poll the
server for possible changes, using the timestamp value from the
previous poll.
If a client only needs data for one time zone (e.g., a clock in a
fixed location), then it can use a conditional HTTP request to
determine if the time zone data has changed and retrieve the new
data. The full details of HTTP conditional requests are described in
[RFC7232], what follows is a brief summary of what a client typically
does. When the client retrieves the time zone data from the server
using a "get" action (see Section 5.3) the server will include an
ETag HTTP header field in the response. The client will store the
value of that header field along with the request-URI used for the
request. When the client wants to check for an update, it issues
another "get" action HTTP request on the original request-URI, but
this time it includes an If-None-Match HTTP request header field,
with a value set to the ETag from the previous response. If the data
for the time zone has not changed, the server will return a 304 (Not
Modified) HTTP response. If the data has changed, the server will
return a normal HTTP success response which will include the changed
data, as well as a new value for the ETag. Thus clients can poll the
server for changes, and only retrieve new data when it is actually
different from what it got before.
Clients SHOULD poll for changes, using an appropriate conditional
request, at least once a day. A server acting as a secondary
provider, caching time zone data from another server, SHOULD poll for
changes once per hour. See Section 8 on expected client and server
behavior regarding high request rates.
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4.1.5. Expanded Time Zone Data
Determining time zone offsets at a particular point in time is often
a complicated process, as the rules for daylight saving time can be
complex. To help with this, the time zone data distribution service
provides an action that allows clients to request the server to
expand a time zone into a set of "observances" over a fixed period of
time (see Section 5.4). Each of these observances describes a UTC
onset time and UTC offsets for the prior time and the observance
time. Together, these provide a quick way for "thin" clients to
determine an appropriate UTC offset for an arbitrary date without
having to do full time zone expansion themselves.
4.1.6. Server Requirements
To enable a simple client implementation, servers SHOULD ensure that
they provide or cache data for all commonly used time zones, from
various publishers. That allows client implementations to configure
a single server to get all time zone data. In turn, any server can
refresh any of the data from any other server - though the root
servers may provide the most up-to-date copy of the data.
4.1.7. Error Responses
The following are examples of response codes one would expect to be
used by the server. Note, however, that unless explicitly prohibited
any 2/3/4/5xx series response code may be used in a response.
200 (OK) - The command succeeded.
304 (Not Modified) - The requested data is unchanged.
400 (Bad Request) - The Sender has provided an invalid request
parameter.
404 (Not Found) - The time zone was not found.
When an HTTP error response is returned to the client, the server
SHOULD return a JSON "problem detail" object in the response body, as
per [I-D.ietf-appsawg-http-problem]. Every JSON "problem detail"
object MUST include a "type" member with a uri value matching the
applicable error code (defined for each action in Section 5).
4.1.8. Extensions
This protocol is designed to be extensible through a standards based
registration mechanism (see Section 9). It is anticipated that other
useful time zone actions will be added in the future (e.g., mapping a
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geographical location to time zone identifiers, getting change
history for time zones), and so, servers MUST return a description of
their capabilities. This will allow clients to determine if new
features have been installed and, if not, fall back on earlier
features or disable some client capabilities.
4.2. Client Guidelines
4.2.1. Discovery
Client implementations need to either know where the time zone data
distribution service is located or discover it through some
mechanism. To use a time zone data distribution service, a client
needs a fully qualified domain name (FQDN), port and HTTP request-URI
path. The request-URI path found via discovery is the "context path"
for the service itself. The "context path" is used as the value of
the "service-prefix" URI template variable when executing actions
(see Section 5).
The following sub-sections describe two methods of service discovery
using DNS SRV records [RFC2782] and an HTTP "well-known" [RFC5785]
resource. However, alternative mechanisms could also be used (e.g.,
a DHCP server option [RFC2131]).
4.2.1.1. Time Zone Data Distribution Service SRV Service Labels
[RFC2782] defines a DNS-based service discovery protocol that has
been widely adopted as a means of locating particular services within
a local area network and beyond, using SRV RR records. This can be
used to discover a service's FQDN and port.
This specification adds two service types for use with SRV records:
timezone: Identifies a Time Zone Data Distribution server that uses
HTTP without transport layer security ([RFC2818]).
timezones: Identifies a Time Zone Data Distribution server that uses
HTTP with transport layer security ([RFC2818]).
Clients MUST honor "TTL", "Priority" and "Weight" values in the SRV
records, as described by [RFC2782].
Example: service record for server without transport layer security.
_timezone._tcp SRV 0 1 80 tz.example.com.
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Example: service record for server with transport layer security.
_timezones._tcp SRV 0 1 443 tz.example.com.
4.2.1.2. Time Zone Data Distribution Service TXT records
When SRV RRs are used to advertise a time zone data distribution
service, it is also convenient to be able to specify a "context path"
in the DNS to be retrieved at the same time. To enable that, this
specification uses a TXT RR that follows the syntax defined in
Section 6 of [RFC6763] and defines a "path" key for use in that
record. The value of the key MUST be the actual "context path" to
the corresponding service on the server.
A site might provide TXT records in addition to SRV records for each
service. When present, clients MUST use the "path" value as the
"context path" for the service in HTTP requests. When not present,
clients use the ".well-known" URI approach described next.
Example: text record for service with transport layer security.
_timezones._tcp TXT path=/timezones
4.2.1.3. Time Zone Data Distribution Service Well-Known URI
A "well-known" URI [RFC5785] is registered by this specification for
the Time Zone Data Distribution service, "timezone" (see Section 9).
This URI points to a resource that the client can use as the initial
"context path" for the service they are trying to connect to. The
server MUST redirect HTTP requests for that resource to the actual
"context path" using one of the available mechanisms provided by HTTP
(e.g., using an appropriate 3xx status response). Clients MUST
handle HTTP redirects on the ".well-known" URI. Servers MUST NOT
locate the actual time zone data distribution service endpoint at the
".well-known" URI as per Section 1.1 of [RFC5785].
Servers SHOULD set an appropriate Cache-Control header field value
(as per Section 5.2 of [RFC7234]) in the redirect response to ensure
caching occurs as needed, or as required by the type of response
generated. For example, if it is anticipated that the location of
the redirect might change over time, then a "no-cache" value would be
used.
To facilitate "context path's" that might differ from user to user,
the server MAY require authentication when a client tries to access
the ".well-known" URI (i.e., the server would return a 401 status
response to the unauthenticated request from the client, then return
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the redirect response after a successful authentication by the
client).
4.2.1.3.1. Example: well-known URI redirects to actual context path
A Time Zone Data Distribution server has a "context path" that is
"/servlet/timezone". The client will use "/.well-known/timezone" as
the path for the service after it has first found the FQDN and port
number via an SRV lookup or via manual entry of information by the
user. When the client makes its initial HTTP request against
"/.well-known/timezone", the server would issue an HTTP 301 redirect
response with a Location response header field using the path
"/servlet/timezone". The client would then "follow" this redirect to
the new resource and continue making HTTP requests there.
4.2.2. Initial Synchronization of All Time Zones
When a secondary service or a client wishing to cache all time zone
data first starts, or wishes to do a full refresh, it synchronizes
with another server by first issuing a "list" action. The client
would preserve the returned datestamp for subsequent use. Each time
zone in the returned list can then be fetched and stored locally. In
addition a mapping of aliases to time zones can be built.
4.2.3. Subsequent Synchronization of All Time Zones
A secondary service or a client caching all time zone data needs to
periodically synchronize with a server. To do so it would issue a
"list" action with the "changedsince" URI query parameter set to the
value of the datestamp returned by the last synchronization. The
client would again preserve the returned datestamp for subsequent
use. Each time zone in the returned list can then be fetched and
stored locally.
Publishers should take into account the fact that the "outright"
deletion of time zone names will cause problems to simple clients and
so aliasing a deleted time zone identifier to a suitable alternate
one is preferable.
5. Actions
Servers MUST support the following actions. The information below
shows details about each action: the request-URI the client targets
(in the form of a URI template [RFC6570]) a description, the set of
allowed query parameters, the nature of the response, and a set of
possible error codes for the response (see Section 4.1.7).
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For any error not covered by the specific error codes defined below,
the "urn:ietf:params:tzdist:error:invalid-action" error code is
returned to the client in the JSON "problem details" object.
5.1. "capabilities" Action
Name: capabilities
Request-URI Template: {/service-prefix}/capabilities
Description: This action returns the capabilities of the server,
allowing clients to determine if a specific feature has been
deployed and/or enabled.
Parameters: None
Response A JSON object containing a "version" member, an "info"
member, and an "actions" member, see Section 6.1.
Possible Error Codes No specific code.
5.1.1. Example: Get Capabilities
>> Request <<
GET /capabilities HTTP/1.1
Host: tz.example.com
>> Response <<
HTTP/1.1 200 OK
Date: Wed, 4 Jun 2008 09:32:12 GMT
Content-Type: application/json; charset="utf-8"
Content-Length: xxxx
{
"version": 1,
"info": {
"primary-source": "Olson:2011m",
"formats": [
"text/calendar",
"application/calendar+xml",
"application/calendar+json"
],
"truncated" : {
"any": false,
"ranges": [
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{
"start": "1970-01-01T00:00:00Z",
"end": "*"
},
{
"start":"2010-01-01T00:00:00Z",
"end":"2020-01-01T00:00:00Z"
}
],
"untruncated": true
},
"provider-details": "http://tz.example.com/about.html",
"contacts": ["mailto:tzs@example.org"]
},
"actions": [
{
"name": "capabilities",
"uri-template": "/capabilities",
"parameters": []
},
{
"name": "list",
"uri-template": "/zones{?changedsince}",
"parameters": [
{
"name": "changedsince",
"required": false,
"multi": false
}
]
},
{
"name": "get",
"uri-template": "/zones{/tzid}{?start,end}",
"parameters": [
{
"name": "start",
"required": false,
"multi": false
},
{
"name": "end",
"required": false,
"multi": false
}
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]
},
{
"name": "expand",
"uri-template":
"/zones{/tzid}/observances{?start,end}",
"parameters": [
{
"name": "start",
"required": true,
"multi": false
},
{
"name": "end",
"required": true,
"multi": false
}
]
},
{
"name": "find",
"uri-template": "/zones{?pattern}",
"parameters": [
{
"name": "pattern",
"required": true,
"multi": false
}
]
}
]
}
5.2. "list" Action
Name: list
Request-URI Template: {/service-prefix,data-
prefix}/zones{?changedsince}
Description: This action lists all time zone identifiers in summary
format, with aliases and optional localized data. In addition, it
returns a timestamp which is the current server last modification
value. If the "changedsince" URI query parameter is present, its
value MUST correspond to a previously returned timestamp value.
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When "changedsince" timestamp is used, the server MUST return only
those time zones that have changed since the specified timestamp.
Parameters:
changedsince OPTIONAL, but MUST occur only once.
Response: A JSON object containing a "dtstamp" member and a
"timezones" member, see Section 6.2.
Possible Error Codes
urn:ietf:params:tzdist:error:invalid-changedsince The
"changedsince" URI query parameter has an incorrect value, or
appears more than once.
5.2.1. Example: List time zone identifiers
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In this example the client requests the time zone identifiers and in
addition requests that the US-English local names be returned.
>> Request <<
GET /zones HTTP/1.1
Host: tz.example.com
>> Response <<
HTTP/1.1 200 OK
Date: Wed, 4 Jun 2008 09:32:12 GMT
Content-Type: application/json; charset="utf-8"
Content-Length: xxxx
{
"dtstamp": "2009-10-11T09:32:11Z",
"timezones": [
{
"tzid": "America/New_York",
"last-modified": "2009-09-17T01:39:34Z",
"aliases":["US/Eastern"],
"local-names": [
{
"name": "America/New_York",
"lang": "en_US"
}
]
},
...
]
}
5.3. "get" Action
Name: get
Request-URI Template: {/service-prefix,data-
prefix}/zones{/tzid}{?start,end}
The "tzid" variable value is REQUIRED to distinguish this action
from the "list" action.
Description: This action returns a time zone. The response MUST
contain an ETag response header field indicating the current value
of the strong entity tag of the time zone resource.
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In the absence of any Accept HTTP request header field, the server
MUST return time zone data with the "text/calendar" media type.
If the "tzid" variable value is actually a time zone alias, the
server will return the matching time zone data with the alias as
the identifier in the time zone data. The server MAY include one
or more "TZID-ALIAS-OF" properties (see Section 7.2) in the time
zone data to indicate additional identifiers that have the
matching time zone identifier as an alias.
Parameters:
start= OPTIONAL, and MUST occur only once. Specifies
the inclusive UTC date-time value at which the returned time
zone data is truncated at its start.
end= OPTIONAL, and MUST occur only once. Specifies
the exclusive UTC date-time value at which the returned time
zone data is truncated at its end.
Response: A document containing all the requested time zone data in
the format specified.
Possible Error Codes
urn:ietf:params:tzdist:error:tzid-not-found No time zone
associated with the specified "tzid" path segment value was
found.
urn:ietf:params:tzdist:error:invalid-format The Accept request
header field supplied by the client did not contain a media
type for time zone data supported by the server.
urn:ietf:params:tzdist:error:invalid-start The "start" URI query
parameter has an incorrect value, or appears more than once, or
does not match one of the fixed truncation range start values
advertised in the "capabilities" action response.
urn:ietf:params:tzdist:error:invalid-end The "end" URI query
parameter has an incorrect value, or appears more than once, or
has a value less than or equal to the "start" URI query
parameter, or does not match one of the fixed truncation range
end values advertised in the "capabilities" action response.
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5.3.1. Example: Get time zone data
In this example the client requests the time zone with a specific
time zone identifier to be returned.
>> Request <<
GET /zones/America%2FNew_York HTTP/1.1
Host: tz.example.com
Accept:text/calendar
>> Response <<
HTTP/1.1 200 OK
Date: Wed, 4 Jun 2008 09:32:12 GMT
Content-Type: text/calendar; charset="utf-8"
Content-Length: xxxx
ETag: "123456789-000-111"
BEGIN:VCALENDAR
...
BEGIN:VTIMEZONE
TZID:America/New_York
...
END:VTIMEZONE
END:VCALENDAR
5.3.2. Example: Conditional Get time zone data
In this example the client requests the time zone with a specific
time zone identifier to be returned, but uses an If-None-Match header
field in the request, set to the value of a previously returned ETag
header field. In this example, the data on the server has not
changed, so a 304 response is returned.
>> Request <<
GET /zones/America%2FNew_York HTTP/1.1
Host: tz.example.com
Accept:text/calendar
If-None-Match: "123456789-000-111"
>> Response <<
HTTP/1.1 304 Not Modified
Date: Wed, 4 Jun 2008 09:32:12 GMT
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5.3.3. Example: Get time zone data using a time zone alias
In this example the client requests the time zone with an aliased
time zone identifier to be returned, and the server returns the time
zone data with that identifier, and two aliases.
>> Request <<
GET /zones/US%2FEastern HTTP/1.1
Host: tz.example.com
Accept:text/calendar
>> Response <<
HTTP/1.1 200 OK
Date: Wed, 4 Jun 2008 09:32:12 GMT
Content-Type: text/calendar; charset="utf-8"
Content-Length: xxxx
ETag: "123456789-000-111"
BEGIN:VCALENDAR
...
BEGIN:VTIMEZONE
TZID:US/Eastern
TZID-ALIAS-OF:America/New_York
TZID-ALIAS-OF:America/Montreal
...
END:VTIMEZONE
END:VCALENDAR
5.3.4. Example: Get truncated time zone data
Assume the server advertises a "truncated" object in its
"capabilities" response that appears as:
"truncated": {
"any": false,
"ranges": [
{"start": "1970-01-01T00:00:00Z", "end": "*"},
{"start":"2010-01-01T00:00:00Z", "end":"2020-01-01T00:00:00Z"}
],
"untruncated": false
}
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In this example the client requests the time zone with a specific
time zone identifier truncated at one of the ranges specified by the
server, to be returned. Note the presence of a "STANDARD" component
that matches the start point of the truncation range (converted to
the local time for the UTC offset in effect at the matching UTC
time). Also, note the presence of the "TZUNTIL" (Section 7.1)
iCalendar property in the "VTIMEZONE" component, indicating the upper
bound on the validity of the time zone data.
>> Request <<
GET /zones/America%2FNew_York
?start=2010-01-01T00:00:00Z
&end=2020-01-01T00:00:00Z
HTTP/1.1
Host: tz.example.com
Accept:text/calendar
>> Response <<
HTTP/1.1 200 OK
Date: Wed, 4 Jun 2008 09:32:12 GMT
Content-Type: text/calendar; charset="utf-8"
Content-Length: xxxx
ETag: "123456789-000-111"
BEGIN:VCALENDAR
...
BEGIN:VTIMEZONE
TZID:America/New_York
TZUNTIL:20191231T111159Z
BEGIN:STANDARD
DTSTART:20101231T190000
TZNAME:EST
TZOFFSETFROM:-0500
TZOFFSETTO:-0500
END:STANDARD
...
END:VTIMEZONE
END:VCALENDAR
5.3.5. Example: Get a non-existent time zone data
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In this example the client requests the time zone with a specific
time zone identifier to be returned.
>> Request <<
GET /zones/America%2FPittsburgh HTTP/1.1
Host: tz.example.com
Accept:application/calendar+json
>> Response <<
HTTP/1.1 404 Not Found
Date: Wed, 4 Jun 2008 09:32:12 GMT
Content-Type: application/problem+json; charset="utf-8"
Content-Language: en
Content-Length: xxxx
{
"type": "urn:ietf:params:tzdist:error:tzid-not-found",
"title": "Time zone identifier was not found on this server",
"status": 404
}
5.4. "expand" Action
Name: expand
Request-URI Template: {/service-prefix,data-prefix}/zones{/tzid}
/observances{?start,end}
The "tzid" variable value is REQUIRED.
Description: This action expands the specified time zone into a list
of onset start date/time (in UTC) and UTC offsets. The response
MUST contain an ETag response header field indicating the current
value of the strong entity tag of the time zone being expanded.
Parameters:
start=: REQUIRED, and MUST occur only once. Specifies
the inclusive UTC date-time value for the start of the period
of interest.
end=: REQUIRED, and MUST occur only once. Specifies
the exclusive UTC date-time value for the end of the period of
interest. Note that this is the exclusive end value - i.e., it
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represents the date just after the range of interest. e.g., if
a client wants the expanded date just for the year 2014, it
would use a start value of "2014-01-01T00:00:00Z" and an end
value of "2015-01-01T00:00:00Z". An error occurs if the end
value is less than or equal to the start value.
Response: A JSON object containing a "tzid" member, and an
"observances" member, see Section 6.3. If the time zone being
expanded is not fully defined over the requested time range (e.g.,
because of truncation), then the server MUST include "start" and/
or "end" members in the JSON response to indicate the actual start
and end point for the observances being returned. The server MUST
include an expanded observance representing the time zone
information in effect at the start of the returned observance
period.
Possible Error Codes
urn:ietf:params:tzdist:error:tzid-not-found No time zone
associated with the specified "tzid" path segment value was
found.
urn:ietf:params:tzdist:error:invalid-start The "start" URI query
parameter has an incorrect value, or appears more than once, or
is missing, or has a value outside any fixed truncation ranges
advertised in the "capabilities" action response.
urn:ietf:params:tzdist:error:invalid-end The "end" URI query
parameter has an incorrect value, or appears more than once, or
has a value less than or equal to the "start" URI query
parameter, or has a value outside any fixed truncation ranges
advertised in the "capabilities" action response..
5.4.1. Example: Expanded JSON Data Format
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In this example the client requests a time zone in the expanded form.
>> Request <<
GET /zones/America%2FNew_York/observances
&start=2008-01-01T00:00:00Z
&end=2009-01-01T00:00:00Z
HTTP/1.1
Host: tz.example.com
>> Response <<
HTTP/1.1 200 OK
Date: Mon, 11 Oct 2009 09:32:12 GMT
Content-Type: application/json; charset="utf-8"
Content-Length: xxxx
ETag: "123456789-000-111"
{
"tzid": "America/New_York",
"observances": [
{
"name": "Standard",
"onset": "2008-01-01T00:00:00Z",
"utc-offset-from": -18000,
"utc-offset-to": -18000
},
{
"name": "Daylight",
"onset": "2008-03-09T07:00:00Z",
"utc-offset-from": -18000,
"utc-offset-to": -14400
},
{
"name": "Standard",
"onset": "2008-11-02T06:00:00Z",
"utc-offset-from": -14400,
"utc-offset-to": -18000
},
]
}
5.5. "find" Action
Name: find
Request-URI Template: {/service-prefix,data-prefix}/zones{?pattern}
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Description: This action allows a client to query the time zone data
distribution service for a matching identifier, alias or localized
name, using a simple "glob" style pattern match against the names
known to the server (with an asterisk * as the wildcard
character). Pattern match strings have the following options:
* not present An exact text match is done, e.g., "xyz"
* first character only An ends-with text match is done, e.g.,
"*xyz"
* last character only A starts-with text match is done, e.g.,
"xyz*"
* first and last characters only A sub-string text match is done,
e.g., "*xyz*"
In addition, when matching, underscore characters (0x5F) SHOULD be
mapped to a single space character (0x20) prior to string
comparison. This allows time zone identifiers such as "America/
New_York" to match a query for "*New York*". ASCII characters in
the range 0x41 ("A") through 0x5A ("Z") SHOULD be mapped to their
lowercase equivalents. To match characters 0x2A ("*") and 0x5C
("\") in the pattern, a single 0x5C ("\") is prepended to act as
an "escaping" mechanism. i.e., a pattern "Test\*" implies an exact
match test against the string "Test*".
Parameters:
pattern= REQUIRED, and MUST occur only once.
Response: The response has the same format as the "list" action,
with one result object per successful match, see Section 6.2.
Possible Error Codes
urn:ietf:params:tzdist:error:invalid-pattern The "pattern" URI
query parameter has an incorrect value, or appears more than
once.
5.5.1. Example: Find action
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In this example the client asks for data about the time zone "US/
Eastern".
>> Request <<
GET /zones&pattern=US/Eastern HTTP/1.1
Host: tz.example.com
>> Response <<
HTTP/1.1 200 OK
Date: Wed, 4 Jun 2008 09:32:12 GMT
Content-Type: application/json; charset="utf-8"
Content-Length: xxxx
{
"dtstamp": "2009-10-11T09:32:11Z",
"timezones": [
{
"tzid": "America/New_York",
"last-modified": "2009-09-17T01:39:34Z",
"aliases":["US/Eastern"],
"local-names": [
{
"name": "America/New_York",
"lang": "en_US"
}
]
},
{
"tzid": "America/Detroit",
"last-modified": "2009-09-17T01:39:34Z",
"aliases":["US/Eastern"],
"local-names": [
{
"name": "America/Detroit",
"lang": "en_US"
}
]
},
...
]
}
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6. JSON Definitions
JSON members used by this specification are defined here using the
syntax in [I-D.newton-json-content-rules]. Clients MUST ignore any
JSON members they do not expect.
6.1. capabilities action response
JSON Content Rules for the JSON document returned for a
"capabilities" action request.
; root object
root {
version,
info,
actions
}
; The version number of the protocol supported - MUST be 1
version "version" : integer 1..1
; object containing service information
info "info" {
primary_source / secondary_source,
formats,
?truncated,
?provider_details,
?contacts
}
; The source of the time zone data provided by a "primary" server
primary_source "primary-source" : string
; The time zone data server from which data is provided by a
; "secondary" server
secondary_source "secondary-source" : uri
; Array of media types for the time zone data formats that the
; server can return
formats "formats" [ 1* : string ]
; Present if the server is providing truncated time zone data. The
; value is an object providing details of the supported truncation
; modes.
truncated "truncated" : {
any,
?ranges,
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?untruncated
}
; Indicates whether the server can truncate time zone data at any
; start or end point. When set to "true" any start or end point is
; a valid value for use with the "start" and "end" URI query
; parameters in a "get" action request
any "any" : boolean
; Indicates which ranges of time the server has truncated data for.
; A value from this list may be used with the "start" and "end" URI
; query parameters in a "get" action request. Not present if "any"
; is set to "true"
ranges "ranges" : [ * : range ]
; A range of time
range {
range-start,
range-end
}
; [RFC3339] UTC date-time value for inclusive start of the range,
; or the single character "*" to indicate a value corresponding to
; the lower bound supplied by the publisher of the time zone data
range-start "start" : date-time
; [RFC3339] UTC date-time value for exclusive end of the range,
; or the single character "*" to indicate a value corresponding to
; the upper bound supplied by the publisher of the time zone data
range-end "end" : date-time
; Indicates whether the server can can supply untruncated data. When
; set to "true" indicates that, in addition to truncated data being
; available, the server can return untruncated data if a "get"
; action request is executed without a "start" or "end" URI query
; parameter
untruncated "untruncated" : boolean
; A URI where human readable details about the time zone service
; is available
provider_details "provider-details" : uri
; Array of URIs providing contact details for the server
; administrator
contacts "contacts" [ * : uri ]
; Array of actions supported by the server
actions "actions" [ * action ]
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; An action supported by the server
action {
action_name,
action_uri_template,
action_params
}
; Name of the action
action_name "name" : string
; URI template for action - this is the URI template from the action
; definitions in Section 5 without the {/service-prefix,data-prefix}
; elements
action_uri_template "uri-template" : string
; Array of request-URI query parameters supported by the action
action_params "parameters" [ * parameter ]
; Object defining an action parameter
parameter {
param_name,
?param_required,
?param_multi,
?param_values
}
; Name of the parameter
param_name "name" : string
; If true the parameter has to be present in the request-URI
; default is false
param_required "required" : boolean
; If true the parameter can occur more than once in the request-URI
; default is false
param_multi "multi" : boolean,
; An array that defines the allowed set of values for the parameter
; In the absence of this member, any string value is acceptable
param_values "values" [ * : string ]
6.2. list/find action response
JSON Content Rules for the JSON document returned for a "list" or
"find" action request.
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; root object
root {
dtstamp,
timezones
}
; Server generated timestamp used for synchronizing changes,
; [RFC3339] UTC value
dtstamp "dtstamp" : date-time
; Array of time zone objects
timezones "timezones" [ * timezone ]
; Information about a time zone available on the server
timezone {
tzid,
last_modified,
?aliases,
?local_names,
}
; Time zone identifier
tzid "tzid" : string
; Date/time when the time zone data was last modified
; [RFC3339] UTC value
last_modified "last-modified" : date-time
; An array that lists the set of time zone aliases available
; for the corresponding time zone
aliases "aliases" [ * : string ]
; An array that lists the set of localized names available
; for the corresponding time zone
local_names "local-names" [ * local_name ]
local_name [lang, lname, ?pref]
; Language tag for the language of the associated name
lang : string
; Localized name
lname : string
; Indicates whether this is the preferred name for the associated
; language default: false
pref : boolean
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6.3. expand action response
JSON Content Rules for the JSON document returned for a "expand"
action request.
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; root object
root {
tzid,
start?,
end?,
observances
}
; Time zone identifier
tzid "tzid" : string
; The actual inclusive start point for the returned observances
; if different from the value of the "start" URI query parameter
start "start" : date-time
; The actual exclusive end point for the returned observances
; if different from the value of the "end" URI query parameter
end "end" : date-time
; Array of time zone objects
observances "observances" [ * observance ]
; Information about a time zone available on the server
observance {
oname,
?olocal_names,
onset,
utc_offset_from,
utc_offset_to
}
; Observance name
oname "name" : string
; Array of localized observance names
olocal_names "local-names" [ * : string]
; [RFC3339] UTC date-time value at which the observance takes effect
onset "onset" : date-time
; The UTC offset in seconds before the start of this observance
utc_offset_from "utc-offset-from" : integer
; The UTC offset in seconds at and after the start of this observance
utc_offset_to "utc-offset-to" : integer
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7. New iCalendar Properties
7.1. Time Zone Upper Bound
Property Name: TZUNTIL
Purpose: This property specifies an upper bound for the validity of
data within a "VTIMEZONE" component.
Value Type: DATE-TIME
Property Parameters: IANA and non-standard property parameters can
be specified on this property.
Conformance: This property can be specified zero or one time within
"VTIMEZONE" calendar components.
Description: The value MUST be specified in the UTC time format.
Time zone data in a "VTIMEZONE" component might cover only a fixed
period of time. The start of such a period is clearly indicated
by the earliest observance defined by the "STANDARD" and
"DAYLIGHT" sub-components. However, [RFC5545] does not define a
way to indicate an upper bound on the validity of the time zone
data, which cannot be simply derived from the observance with the
latest onset time. This specification introduces the "TZUNTIL"
property for that purpose. It specifies an "inclusive" UTC date-
time value that indicates the last time at which the time zone
data is to be considered valid.
This property is also used by time zone data distribution servers
to indicate the truncation range end point of time zone data (as
described in Section 3.8).
Format Definition: This property is defined by the following
notation:
tzuntil = "TZUNTIL" tzuntilparam ":" date-time CRLF
tzuntilparam = *(";" other-param)
Example: Suppose a time zone based on astronomical observations has
well-defined onset times through the year 2025, but the first
onset in 2026 is currently known only approximately. In that
case, the "TZUNTIL" property could be specified as follows:
TZUNTIL:20251231T235959Z
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7.2. Time Zone Identifier Alias Property
Property Name: TZID-ALIAS-OF
Purpose: This property specifies a time zone identifier that the
main time zone identifier is an alias of.
Value Type: TEXT
Property Parameters: IANA and non-standard property parameters can
be specified on this property.
Conformance: This property can be specified zero or more times
within "VTIMEZONE" calendar components.
Description: When the "VTIMEZONE" component uses a time zone
identifier alias for the "TZID" property value, the "TZID-ALIAS-
OF" property is used to indicate the time zone identifier of the
other time zone (see Section 3.6).
Format Definition: This property is defined by the following
notation:
tzid-alias-of = "TZID-ALIAS-OF" tzidaliasofparam ":"
[tzidprefix] text CRLF
tzidaliasofparam = *(";" other-param)
;tzidprefix defined in [RFC5545].
Example: The following is an example of this property:
TZID-ALIAS-OF:America/New_York
8. Security Considerations
Time zone data is critical in determining local or UTC time for
devices and in calendaring and scheduling operations. As such, it is
vital that a reliable source of time zone data is used. Servers
providing a time zone data distribution service MUST support HTTP
over Transport Layer Security (TLS) (as defined by [RFC2818]) with a
valid certificate. Clients and servers making use of a time zone
data distribution service SHOULD use HTTP over TLS and verify the
authenticity of the service being used before accepting and using any
time zone data from that source.
Clients that support transport layer security as defined by [RFC2818]
SHOULD try the "_timezones" service first before trying the
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"_timezone" service. Clients MUST follow the certificate
verification process specified in [RFC6125].
A malicious attacker with access to the DNS server data, or able to
get spoofed answers cached in a recursive resolver, can potentially
cause clients to connect to any server chosen by the attacker. In
the absence of a secure DNS option, clients SHOULD check that the
target FQDN returned in the SRV record matches the original service
domain that was queried. If the target FQDN is not in the queried
domain, clients SHOULD verify with the user that the SRV target FQDN
is suitable for use before executing any connections to the host.
Time zone data servers SHOULD protect themselves against errant or
malicious clients by throttling high request rates or frequent
requests for large amounts of data. Clients can avoid being
throttled by using the polling capabilities outlined in
Section 4.1.4. Servers MAY require some form of authentication or
authorization of clients (including secondary servers) to restrict
which clients are allowed to access their service, or provide better
identification of errant clients. As such, servers MAY require HTTP-
based authentication as per [RFC7235].
9. IANA Considerations
This specification defines a new registry of "actions" for the time
zone data distribution service protocol, defines a "well-known" URI
using the registration procedure and template from Section 5.1 of
[RFC5785], creates two new SRV service label aliases, and defines one
new iCalendar property parameter as per the registration procedure in
[RFC5545]. It also adds a new "tzdist" sub-namespace to the IETF
parameters URN sub-namespace as per [RFC3553] for use with protocol
related error codes.
9.1. Service Actions Registration
This section defines the process to register new or modified time
zone data distribution service actions with IANA.
9.1.1. Service Actions Registration Procedure
The IETF will create a mailing list, tzdist-service@ietf.org, which
can be used for public discussion of time zone data distribution
service actions proposals prior to registration. Use of the mailing
list is strongly encouraged. The IESG will appoint a designated
expert who will monitor the tzdist-service@ietf.org mailing list and
review registrations.
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Registration of new time zone data distribution service actions MUST
be reviewed by the designated expert and published in an RFC. A
Standard Track RFC is REQUIRED for the registration of new time zone
data distribution service actions. A Standard Track RFC is also
REQUIRED for changes to actions previously documented in a Standard
Track RFC.
The registration procedure begins when a completed registration
template, as defined below, is sent to tzdist-service@ietf.org and
iana@iana.org. The designated expert is expected to tell IANA and
the submitter of the registration within two weeks whether the
registration is approved, approved with minor changes, or rejected
with cause. When a registration is rejected with cause, it can be
re-submitted if the concerns listed in the cause are addressed.
Decisions made by the designated expert can be appealed to the IESG
Applications Area Director, then to the IESG. They follow the normal
appeals procedure for IESG decisions.
9.1.2. Registration Template for Actions
An action is defined by completing the following template.
Name: The name of the action.
Request-URI Template: The URI template used in HTTP requests for the
action.
Description: A general description of the action, its purpose, etc.
Parameters: A list of allowed request URI query parameters,
indicating whether they are "REQUIRED" or "OPTIONAL" and whether
they can occur only once or multiple times, together with the
expected format of the parameter values.
Response The nature of the response to the HTTP request, e.g., what
format the response data is in.
Possible Error Codes Possible error codes reported in a JSON
"problem details" object if an HTTP request fails.
9.2. Initial Time Zone Data Distribution Service Registry
The IANA is requested to create and maintain the following registry
for time zone data distribution service actions with pointers to
appropriate reference documents.
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9.2.1. Actions Registry
The following table is to be used to initialize the actions registry.
+---------------+----------+-----------------------+
| Action Name | Status | Reference |
+---------------+----------+-----------------------+
| capabilities | Current | RFCXXXX, Section 5.1 |
| list | Current | RFCXXXX, Section 5.2 |
| get | Current | RFCXXXX, Section 5.3 |
| expand | Current | RFCXXXX, Section 5.4 |
| find | Current | RFCXXXX, Section 5.5 |
+---------------+----------+-----------------------+
9.3. timezone Well-Known URI Registration
URI suffix: timezone
Change controller: IETF.
Specification document(s): This RFC.
Related information:
9.4. Service Name Registrations
This document registers two new service names as per [RFC6335]. Both
are defined within this document.
9.4.1. timezone Service Name Registration
Service Name: timezone
Transport Protocol(s): TCP
Assignee: IESG
Contact: IETF Chair
Description: Time Zone Data Distribution Service - non-TLS
Reference: [This Draft]
Assignment Note: This is an extension of the http service. Defined
TXT keys: path=
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9.4.2. timezones Service Name Registration
Service Name: timezones
Transport Protocol(s): TCP
Assignee: IESG
Contact: IETF Chair
Description: Time Zone Data Distribution Service - over TLS
Reference: [This Draft]
Assignment Note: This is an extension of the https service. Defined
TXT keys: path=
9.5. tzdist URN sub-namespace
IANA is requested to register a new URN sub-namespace within the IETF
URN Sub-namespace for Registered Protocol Parameter Identifiers
defined in [RFC3553].
Registry name: tzdist
Specification): This RFC
Repository: Time Distribution Service protocol elements registry.
Index value:: This specification defines the single "error" sub-
parameter, which itself has sub-parameters representing specific
error codes within the protocol as defined in the list of actions
in Section 5 and used in problem reports (Section 4.1.7).
9.6. iCalendar Property Registrations
This document defines the following new iCalendar properties to be
added to the registry defined in Section 8.2.3 of [RFC5545]:
+----------------+----------+-----------------------+
| Property | Status | Reference |
+----------------+----------+-----------------------+
| TZUNTIL | Current | RFCXXXX, Section 7.1 |
| TZID-ALIAS-OF | Current | RFCXXXX, Section 7.2 |
+----------------+----------+-----------------------+
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10. Acknowledgements
The authors would like to thank the members of the Calendaring and
Scheduling Consortium's Time Zone Technical Committee, and the
participants and chairs of the IETF tzdist working group. In
particular, the following individuals have made important
contributions to this work: Steve Allen, Lester Caine, Stephen
Colebourne, Tobias Conradi, Steve Crocker, Paul Eggert, John Haug,
Ciny Joy, Bryan Keller, Andrew McMillan, Ken Murchison, Tim Parenti,
Arnaud Quillaud, Jose Edvaldo Saraiva, and Dave Thewlis.
This specification originated from work at the Calendaring and
Scheduling Consortium, which has supported the development and
testing of implementations of the specification.
11. References
11.1. Normative References
[I-D.ietf-appsawg-http-problem]
Nottingham, M. and E. Wilde, "Problem Details for HTTP
APIs", draft-ietf-appsawg-http-problem-00 (work in
progress), September 2014.
[I-D.newton-json-content-rules]
Newton, A., "A Language for Rules Describing JSON
Content", draft-newton-json-content-rules-03 (work in
progress), October 2014.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the
Internet: Timestamps", RFC 3339, July 2002.
[RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
IETF URN Sub-namespace for Registered Protocol
Parameters", BCP 73, RFC 3553, June 2003.
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[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5545] Desruisseaux, B., "Internet Calendaring and Scheduling
Core Object Specification (iCalendar)", RFC 5545,
September 2009.
[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785, April
2010.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011.
[RFC6321] Daboo, C., Douglass, M., and S. Lees, "xCal: The XML
Format for iCalendar", RFC 6321, August 2011.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165, RFC
6335, August 2011.
[RFC6557] Lear, E. and P. Eggert, "Procedures for Maintaining the
Time Zone Database", BCP 175, RFC 6557, February 2012.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570, March 2012.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, February 2013.
[RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, March 2014.
[RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Message Syntax and Routing", RFC 7230, June
2014.
[RFC7231] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Semantics and Content", RFC 7231, June 2014.
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[RFC7232] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Conditional Requests", RFC 7232, June 2014.
[RFC7234] Fielding, R., Nottingham, M., and J. Reschke, "Hypertext
Transfer Protocol (HTTP/1.1): Caching", RFC 7234, June
2014.
[RFC7235] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Authentication", RFC 7235, June 2014.
[RFC7265] Kewisch, P., Daboo, C., and M. Douglass, "jCal: The JSON
Format for iCalendar", RFC 7265, May 2014.
11.2. Informative References
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
Appendix A. Change History (to be removed prior to publication as an
RFC)
Changes for -04
1. Tweaked invalid-start/end for action expand to indicate outside
truncation range.
2. Added text on use of Accept-Language.
3. Added text on requirement to percent-encode {/tzid}.
4. Moved /observances under /zones{/tzid}.
5. Observances response now includes start/end of actual range
returned if different from what was requested.
6. Truncation end and &end= for get action are now exclusive.
7. Added capabilities action in capabilities example response.
8. Added uri-template items to capabilities action definitions.
9. Added start/end items to the observances response.
10. Error codes are now URNs (with an IANA registration for a tzdist
sub-namespace) and the URNs are used as the type value in JSON
problem reports.
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11. Removed "changedsince" from expand action - ETag can be used
instead.
Changes for -03
1. Reworked conditional list section
(https://tools.ietf.org/wg/tzdist/trac/ticket/22 &
https://tools.ietf.org/wg/tzdist/trac/ticket/33).
2. Moved definitions into General Considerations section.
3. Now makes use of ietf-appsawg-http-problem for error responses.
4. Switched to using a more RESTful design with resources used to
identify endpoints for actions
(https://tools.ietf.org/wg/tzdist/trac/ticket/29).
5. Tweaked TZUNTIL text to further address
(https://tools.ietf.org/wg/tzdist/trac/ticket/15).
6. Tweaked "outright" deletion text to match latest on mailing list
(https://tools.ietf.org/wg/tzdist/trac/ticket/18).
7. Added additional text suggesting other discovery mechanisms could
be used (https://tools.ietf.org/wg/tzdist/trac/ticket/30).
8. Now require "end" parameter on expand to avoid issues with
truncated data upper bounds
(https://tools.ietf.org/wg/tzdist/trac/ticket/10).
Changes for -02
1. "time zone server" -> "time zone data server".
2. Re-worded some text containing reference to "historical" time
zone data, and truncation behavior.
3. Removed "REST".
4. Use "TZID-ALIAS-OF" in place of "EQUIVALENT-TZID".
5. Added \-escape mechanism for find action.
6. Revised Section 4.2.3 to address
(https://tools.ietf.org/wg/tzdist/trac/ticket/18).
Changes for -01
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1. Query attribute: "name" -> "pattern"
(https://tools.ietf.org/wg/tzdist/trac/ticket/4).
2. UTF-8 used for time zone ids and in all responses.
3. Added glossary term and note for "time zone"
(https://tools.ietf.org/wg/tzdist/trac/ticket/12).
4. Glossary term change and alias text from
(https://tools.ietf.org/wg/tzdist/trac/ticket/13).
5. "Local Provider" -> "Secondary Provider".
6. Additional security text for
(https://tools.ietf.org/wg/tzdist/trac/ticket/25).
7. Added additional text to better describe localized names.
8. Added "tzid" member to expand response.
9. Added optional "provider-details" member to capabilities
response, and also made "contacts" optional.
10. Definition of "invalid-action" moved to Section 6, and clarified
text related to error responses in Sections 4.1.6 and 6
(https://tools.ietf.org/wg/tzdist/trac/ticket/17).
11. Added "Observance" to glossary.
12. Added "TZUNTIL" iCalendar property (part of
https://tools.ietf.org/wg/tzdist/trac/ticket/15).
13. Revamped truncation to always use UTC date-time values and
support end points (https://tools.ietf.org/wg/tzdist/trac/
ticket/21, and https://tools.ietf.org/wg/tzdist/trac/ticket/10).
14. Expand always uses UTC date-time values for query parameters,
and always returns UTC date-time onset values
(https://tools.ietf.org/wg/tzdist/trac/ticket/21).
Changes for -00
1. Initial WG draft derived from draft-douglass-timezone-service-11,
with some terminology changes to match WG name.
2. Updated references.
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3. "timezone" -> "time zone" (https://tools.ietf.org/wg/tzdist/trac/
ticket/6).
4. Glossary tweak (first part of
https://tools.ietf.org/wg/tzdist/trac/ticket/13).
5. Fix iCalendar property names: UTC-OFFSET-* -> TZOFFSET*.
6. Fix invalid-truncate error code description.
Authors' Addresses
Michael Douglass
Rensselaer Polytechnic Institute
110 8th Street
Troy , NY 12180
USA
Email: douglm@rpi.edu
URI: http://www.rpi.edu/
Cyrus Daboo
Apple Inc.
1 Infinite Loop
Cupertino , CA 95014
USA
Email: cyrus@daboo.name
URI: http://www.apple.com/
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